In a computer network in which a plurality of clients communicate with one or more servers, a protocol is necessary to establish the rules by which the information is transmitted to effect such communication. Generally, the information is sent from the server in successive packets of information, with each of the packets transversing their own paths through the network, until such time as the packets are reassembled at the destination client. To establish the communication, each packet contains, in addition to a data segment of the total information to be sent, the source address of the server in the network and the destination address of the client in the network.
A commonly used protocol used to establish these connections is the Transmission Control Protocol (“TCP”). TCP is used along with the Internet Protocol (“IP”) to send data in the form of message units between computers over the Internet. While IP takes care of handling the actual delivery of the data, TCP takes care of keeping track of the packets that a message is divided into for efficient routing through the Internet.
For example, when an HTML file is sent from a web server, the TCP program layer in that server divides the file into one or more packets, numbers the packets, and then forwards them individually to the IP program layer. Although each packet has the same destination IP address, each packet may get routed differently through the network. At the client, TCP reassembles the individual packets and waits until they have arrived to display the re-assembled HTML file.
TCP is also known as a connection-oriented protocol, which means that a connection is established and maintained until such time as the message or messages to be exchanged by the application programs at each end of the connection have been exchanged. TCP is responsible for ensuring that a message is divided into the packets that IP manages and for reassembling the packets back into the complete message at the other end.
Another protocol to transmit information is the User Datagram Protocol (“UDP”). UDP is a communications method that offers a limited amount of service when messages are exchanged between computers in a network that uses IP. UDP is an alternative to TCP and, together with IP, is sometimes referred to as UDP/IP. Like TCP, UDP uses the IP to actually get a data unit, or datagram, from one computer to another.
Unlike TCP, however, UDP does not provide the service of dividing a message into packets or datagrams, and reassembling them at the other end. Specifically, UDP does not provide sequencing of the packets that the data arrives in. Accordingly, the application program that uses UDP must be able to ascertain that the entire message has arrived and is in the right order. Network applications that want to save processing time because they have very small data units to exchange (and therefore very little message reassembling to do) may usually use UDP instead of TCP. UDP does provide two services not provided by the IP layer. It provides a port number to help distinguish different user requests and, optionally, a checksum capability to verify that the data arrived intact.
For streaming applications over a computer network, both UDP and TCP have significant disadvantages and limitations. For example, since TCP requires that all packets are received prior to reassembly at the client, any missing packets could cause the streaming application running at the client to be paused due to the lack of data. UDP also requires that all of the packets are received and also received in the right order, since there is no sequencing of the packets. For a large number of packets in a streaming application, the packets may arrive out of order, resulting in degradation of the output of the streaming application.
Other features of TCP further disadvantageously limit the ability to deliver packets for streaming applications in a timely manner. For example, TCP requires that each packet sent in the stream must be received and each packet delivered to the client in the order sent. This requirement of TCP is especially limiting and disadvantageous for a streaming application. If the server sends four sequential packets, and packet 1 is lost, the client running the streaming application cannot receive the remaining three packets from the TCP protocol stack until it receives the first packet. If the client receives the first packet sufficiently late, all the previously received packets may be useless due to the tardy reception. In any event, the output of the streaming application will be degraded or possibly halted.
There is therefore needed a connectionless protocol which overcomes one or more disadvantages and limitations of the prior art herein above enumerated.